JPH05299719A - Stacked actuator element and manufacture of the same - Google Patents

Abstract

PURPOSE:To improve moisture resistant load life of a stacked type piezoelectric actuator. CONSTITUTION:After an element 8 is eletrostatically painted with an external loading resin 10, the element is hardened by the heat treatment. In this case, the element is hardened by the heat treatment under the vacuum atmosphere, without leaving bubbles within the external loading resin 10. Otherwise, after the element is hardened by the heat treatment under the atmospheric condition, like the existing method, the liquid resin 12 is supplied with pressure to eliminate bubbles within the external loading resin 10. Thereby, since any bubbles are not left in the external loading resin, even if the external loading resin absorbes the moisture in the air during operation of element, quantity of saturated and absorbed water content can be reduced and moisture resistant load life can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric actuator element and its manufacturing method, and more particularly to an element structure and manufacturing method for improving its reliability.

[0002]

2. Description of the Related Art A conventional laminated piezoelectric actuator element (hereinafter referred to as an element) has a structure shown in FIG. 5 through various steps shown in FIG. (For example, JP-A-5
7-79034, as a reference, "Multilayer Piezoel
ectric Ceramic Actuators and The Applications 」Jp
nJAppl.Phys., Vol.24. Suppl. 24-2, p41 (1985). ) FIG. 4 is a process diagram showing a conventional device manufacturing method, and FIG. 5 is a perspective view showing the state of the device during the manufacturing process.

First, as shown in FIG. 4, after making a slurry by kneading a piezoelectric ceramic powder and a solvent in a kneading step A, 100 to 20 in a thick film ceramic sheet forming step B.
A 0 μm ceramic sheet is formed. Next, in the electrode paste printing step C, 1 electrode paste is applied on the ceramic sheet.
Printing is performed to a thickness of 0 to 20 μm, and the sheet is punched into a predetermined size in the sheet punching step D. After this, several tens of sheets punched out in the laminating press step E are laminated and pressed, and then sintered at a high temperature in a sintering step F to form a ceramic sheet 2 and internal electrodes 3 as shown in FIG. A sintered body 1 in which a large number of are laminated is obtained.

Next, in a block cutting step G, the sintered body 1 is cut into strip-shaped blocks 4 as shown in FIG. 5 (b), and then in a glass insulating portion forming step H as shown in FIG. 5 (b). The exposed portions of the internal electrodes 3 exposed on the cut surface of the block 4 are covered with the glass insulating portion 5 every other layer.

Next, in an external electrode forming step J, external electrodes 6 are formed on the side surfaces of the block 4 as shown in FIG. 5B, and the exposed portions of the internal electrodes 3 exposed on the side surfaces are electrically separated by one layer. Connect to.

Thereafter, the element cutting step K is started and the block 4
5 is cut into individual element pieces along a cutting portion 9 shown in FIG. 5B with a multi-wire saw, and the lead wire 7 is soldered to the external electrode 6 in the lead attaching step L. Next, in the electrostatic coating process M, the resin is electrostatically coated, and in the resin curing process N, the exterior resin is heated and cured in the atmosphere to complete the element 8.

[0007]

By the way, the element 8 obtained by the above-mentioned manufacturing method has insufficient reliability as described below.

First, a reliability test was conducted on the conventional element 8. The test is a humidity resistance load life test, 65 ° C 95% RH
Under the environmental conditions, the rated DC voltage is continuously applied, and the short circuit failure is detected by blowing the fuse connected in series to the element 8. The test results are shown in FIG. In the conventional device, the first failure occurred 50 to 100 hours after the start of the test, about 50% became defective after about 500 hours, and the total number became defective after about 1000 hours.

Most of the defective elements caused discharge breakdown on the exposed surface S of the internal electrode shown in FIG. 5 (c). As a result of investigating the cause of this discharge, the following factors were found to be statistically significant.

(1) In the device manufacturing process shown in FIG. 4, after the device cutting process K, the internal surface of the cutting surface 13 shown in FIG. 5 is exposed.

(2) After cutting the element into individual pieces, the lead wire is soldered and the element body is covered with the exterior resin. The exterior resin is heated and cured and then polished, and the inside of the resin is observed. As a result, the element 8 in FIG. 6 is obtained. As shown in the vertical sectional view of FIG.
Contains a large number of bubbles 11 with a diameter of 100 μm,
It is, so to speak, a porous property and it is easy for moisture in the atmosphere to easily enter.

(3) The saturated water supply amount of the exterior resin has a strong correlation with the size of bubbles in the exterior resin and the number of bubbles generated per unit weight. That is, the saturated water absorption amount of the exterior resin per unit weight increases as the size of the bubbles in the exterior resin relatively increases and the number of bubbles per unit weight increases.

(4) The size and the number of bubbles in the exterior resin are not constant because they are affected by the fluctuation of the working conditions in the exterior resin process. However, the larger the size and the number of bubbles, the more the discharge in the moisture resistance load life test. The time it takes to get there tends to be short.

[0014]

In the method of manufacturing a laminated piezoelectric actuator element according to the present invention, generation of bubbles in the exterior resin is prevented, or bubbles generated in the exterior resin are extinguished later. Thus, an element in which air bubbles are not contained in the exterior resin is provided.

[0015]

With the above structure, since the exterior resin of the piezoelectric actuator element does not contain air bubbles, when moisture in the atmosphere enters the exterior resin, the saturated water absorption amount per unit weight of the resin is significantly reduced. Therefore, the moisture reaching the exposed surface of the element of the internal electrode is reduced, and the moisture resistance load life of the element is improved.

[0016]

First Embodiment An optimum embodiment of the present invention will be described below with reference to the drawings.

FIG. 1A is a vertical sectional view of an element showing an embodiment of the present invention. In this example, an element was formed under the conditions described below according to the manufacturing process shown in FIG. 2, and a reliability test was performed to confirm the effect.

In the following description of manufacturing, reference is also made to FIG. 5 described above, and similar steps are designated by the same reference numerals. First, the powder of the piezoelectric ceramic, the solvent, and the powder are kneaded, and then a ceramic sheet of about 130 μm is formed. Next, 1 electrode paste is applied on the ceramic sheet 2.
After printing with a thickness of 0 μm to form the internal electrodes 3, this sheet is punched to a predetermined size, and 130 sheets are laminated and pressed to form a pressed body. Next, press this 11
After firing at 20 ° C. for 2 hours to obtain a sintered body as shown in FIG. 5 (a), a block 4 on a strip as shown in FIG. 5 (b).
Disconnect.

Next, glass insulating portions 5 are formed on every other layer on the internal electrodes 3 exposed on one cut surface of the block 4 on the strip. Next, the glass insulating portions 5 are formed on every other internal electrode exposed on the other cut surface. After that, the external electrodes 6 are provided on the two side surfaces on which the glass insulating portion 5 is formed, and each element 8 is cut by a multi-wire saw and divided. Next, the lead wire 7 is soldered to the external electrode 6 and the exterior resin is electrostatically coated, and then the exterior resin is cured. The curing procedure will be described below.

First, the element after electrostatic coating is set in a vacuum heating oven. Next, the pressure in the oven is set to 1T.
The pressure is set to a low pressure of orr or less, and while maintaining the low pressure, the resin is heated to the resin curing temperature and held for a certain period of time. Then, the temperature in the oven is lowered to room temperature to complete the device. At the time of cooling, the pressure in the oven may be atmospheric pressure, or 1 Torr
The temperature may be lowered at the following low pressure and then returned to atmospheric pressure.

Next, the saturated water absorption of the exterior resin of the completed element was investigated. As a saturated water vapor measurement condition, the completed element was left in an atmosphere of 40 ° C. and 95% RH for 100 hours,
Then, it was taken out and the amount of water in the resin was measured by the Karl Fischer method to compare the saturated water absorption with the element of the conventional method.

As a result of the measurement, the conventional method element had a water absorption rate of about 0.5% per unit weight of the exterior resin, whereas
The element produced by this proposal was about 0.1%, and the water absorption rate was significantly reduced as compared with the conventional element. Next, the result of the reliability test performed on the completed element 8 will be described. The reliability is determined under the environment of 65 ° C. and 95% RH by applying the rated DC voltage to the element 8 and detecting the failure of the element 8 depending on whether the fuse connected in series to the element 8 is blown or not. The relationship between the test time until occurrence and the cumulative defective rate was plotted in the figure and judged.

The test results are shown in FIG. From the figure, in the device according to the present example, the defects were generated later than the above-described conventional device, and the first defects were generated 300 to 400 hours after the start of the test, and a total of 50% became defective in 2000 hours.
The result was that all of them became defective at 00 hours.

[0024]

Second Embodiment The second embodiment is characterized in that the exterior resin is electrostatically coated by a conventional method, then cured, and then a low-viscosity liquid resin is injected into the bubbles in the exterior resin. Figure 1 (b)
Sectional drawing of Example 2 is shown in FIG. First, according to the conventional method, an element which has been exposed to electrostatic coating and cured by resin is set in a pressure vessel, and the pressure in the pressure vessel is set to 10 Torr or less. After that, a low-viscosity liquid resin (for example, an epoxy resin or a silicon resin) that has been degassed in advance is introduced into the container, and the inside of the pressure container is pressurized to 100 to 1000 atm. Then, the pressure inside the container is returned to atmospheric pressure, the liquid resin is extracted from the container, and then the element is taken out from the container. After wiping off the liquid resin adhering to the surface of the device, if necessary, heating is applied to cure the liquid resin to complete the device. When the same test as in Example 1 is carried out using the element manufactured according to Example 2, in comparison with the conventional element in any of the saturated water absorption amount per unit weight of resin and the moisture resistance load life test, As well as greatly improved.

[0025]

As described above, since the exterior resin of the piezoelectric actuator element manufactured by the method of the present invention does not contain air bubbles, when moisture in the atmosphere penetrates into the exterior resin, The amount of saturated water absorption is significantly reduced, so that moisture reaching the surface of the exposed element of the internal electrode is reduced, and the moisture resistance load life of the element is improved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a laminated piezoelectric actuator showing an embodiment of the present invention (a) An element showing the embodiment 1. FIG. (B) A longitudinal sectional view of the element showing the second embodiment.

FIG. 2 is a block diagram showing a manufacturing process according to the first embodiment of the present invention.

FIG. 3 is a characteristic factor diagram showing reliability test results of an element according to Example 1 of the present invention and an element according to a conventional manufacturing method.

FIG. 4 is a block diagram showing a manufacturing process of a conventional element.

FIG. 5 is a perspective view of an element in a conventional manufacturing process of the element.

FIG. 6A is a sectional view of a conventional element. (B) A partially enlarged view of FIG.

[Explanation of symbols]

 1 Sintered Body 2 Ceramic Sheet 3 Internal Electrode 4 Block 5 Glass Insulation Part 6 External Electrode 7 Lead Wire 8 Element 9 Cutting Part 10 Exterior Resin 11 Bubble 12 Liquid Resin 13 Cut Surface

Claims (3)

[Claims] 1. A step of dividing a sintered body obtained by alternately stacking and sintering piezoelectric ceramic sheets and internal electrode layers into blocks, and exposing the side surfaces of the block on opposite side surfaces of the block. After coating the electrode portion with an insulator every other layer, a step of providing an external electrode on the side surface, a step of cutting the block provided with the external electrode to divide into a minimum unit of element pieces, In a method of manufacturing a laminated piezoelectric actuator, which includes a step of connecting a lead wire to an element piece and applying an exterior, manufacturing of the laminated piezoelectric actuator element, wherein heat curing of the exterior resin is performed in a vacuum atmosphere. Method. 2. In the method for manufacturing a laminated piezoelectric actuator element, bubbles in the exterior resin generated when the exterior resin is cured are eliminated by press-fitting a low-viscosity liquid insulating resin from the surface of the exterior resin after the exterior resin is cured. A method of manufacturing a laminated actuator element, comprising: 3. A laminated piezoelectric actuator element characterized in that the exterior resin does not contain bubbles having an inner diameter of about 10 μm or more.